Virtue, then, is of two kinds, intellectual and moral. Intellectual virtue owes its birth and its growth chiefly to teaching, and for this reason requires experience and time; whereas moral virtue is the product of habit, from which it has actually taken its name, being a slight modification of the word ethos. From this it is also clear that none of the moral virtues is instilled in us by nature: for nothing that exists by nature can be altered by habit. Thus a stone, which by nature moves downwards, cannot be habituated to move upwards, not even if one were to try to train it by throwing it up ten thousand times; nor can fire be habituated to move downwards, and nothing that has a given nature can be habituated to behave differently. Consequently, virtues are present in neither by nature nor contrary to nature, but we are naturally adapted to receive them, and we make them perfect through habit.

Moreover, in the case of all natural faculties, we first acquire the potentials, and subsequently display the corresponding activities. This is clearly seen in the case of the senses: it is not by frequently seeing or frequently hearing that we have acquired sight or hearing, but, on the contrary, we already had these senses before using them, and we did not acquire them after having used them. With virtues, the opposite is true: we acquire them by first exercising them, just as it is also with the arts. Indeed, things that we have to learn before we can do them, we learn by doing them. For example, men become builders by building, and cithara-players by playing the cithara. Thus, too, by doing just acts we become just, by doing temperate acts we become temperate, by doing courageous acts we become courageous. This is confirmed by what happens in states: legislators make citizens good by habituating them, and this is the intention of every legislator; if he fails to do this well, he misses his mark, and it is in this that a good constitution differs from a bad one.

Furthermore, every virtue is produced and destroyed by the same causes and through the same means, and similarly every art. For it is by playing the cithara that both good and bad cithara-players are produced, and it is the same with builders and all other craftsmen: by building well one will become a good builder, by building badly a bad one. Indeed, if this were not so, there would be no need of a teacher, and everyone would be born either a good or a bad craftsman. The same is true of virtues: it is by acting in our transactions with other men that some of us become just and others unjust; by acting in dangerous situations and habituating ourselves to feel fear or confidence, some of us become courageous and others cowardly; and the same applies to desires and anger: some become temperate and gentle, others intemperate and irascible, according as they behave in one way or another in the circumstances corresponding to these passions. In a word, moral dispositions are engendered by similar activities. That is why we must make our activities of a certain quality, since the difference in our moral habits corresponds to the differences in our activities. Thus it is no small matter whether we are habituated this way or that straight from our youth; on the contrary, it is of very great importance, or rather it is everything.